Plant cognition






  • Do plants sense their environment?
    • changes in essential resources
    • herbivory/disturbance
    • external stimuli


  • If so, what do they do about it?
    • do plants process information?

Sensory cell systems - Sensing environmental stimuli


  • Cell to cell signaling via plasmodesmata
    • Ca2+ based signals are common


  • Vascular tissues provide long-distance transport


Wounding triggers transmission of Ca2+ to start defense


Plants grow towards light: Phototropism via Auxin hormone

Plants competing for light can grow really tall




  • Primary and secondary growth allow trees to be giants
    • meristems + cambium


  • Are their limitations to plant height?
    • Tallest redwood tree = 116 m


  • What resource most limits growth?

Plant Water Transport: Soil → Root → Stem → Leaf → Air

Are there limits to moving water?



  • Large trees may move hundreds of gallons of water a day
    • only small amounts needed for growth/photosynthesis


  • Gravity does not help
    • harder and harder to move water up
    • xylem become less efficient @ top


  • Drying soil adds opposite tension
    • water potential of soil becomes more negative

How long a straw could Superman use?

How can redwood trees grow so tall?


  • Transpiration pulls water under tension
    • creates ‘capillary action’


  • Cohesion-tension theory
    • properties of water help to cheat gravity


  • Cohesion: H20 molecules stick together
    • via Hydrogen bonds


  • Adhesion: water sticks to non-water molecules
    • stick to sides of xylem tissues
    • H20 not pulled straight up!

How can redwood trees grow so tall?



  • H2O also pulled in zig zag motion
    • pits (holes) in all xylem cells
    • tracheids are twisted


  • Vascular tissue is tough
    • high resistance of lignified walls
    • built not to collapse under tension


  • Redwoods near theoretical limit!!!

Cavitation: When water under tension breaks (cohesion fails)

When to much tension breaks the ‘string’ of water, an air bubble is introduced

How plants avoid water problems: Close stomata

Stomatal behavior: play it safe vs risky

How plants avoid water problems: Refill soil water at night

How plants avoid water problems: Taper xylem cell shape